Fixes #25342.
Still not sure on the exact user agent to set (should it include
`node`?).
After this PR, here's the state of running some `create-*` packages
(just ones I could think of off the top of my head):
| package | prints/runs/suggests deno install | notes |
| ---------------- | ------------- | ------ |
| `create-next-app` | ❌ | falls back to npm, needs a PR
([code](c32e280209/packages/create-next-app/helpers/get-pkg-manager.ts (L3)))
| `sv create` | ❌ | uses `package-manager-detector`, needs a PR
([code](https://github.com/antfu-collective/package-manager-detector/tree/main))
| `create-qwik` | ✅ | runs `deno install` but suggests `deno start`
which doesn't work (should be `deno task start` or `deno run start`)
| `create-astro` | ✅ | runs `deno install` but suggests `npm run dev`
later in output, probably needs a PR
| `nuxi init` | ❌ | deno not an option in dialog, needs a PR
([code](f04e2e8944/src/commands/init.ts (L96-L102)))
| `create-react-app` | ❌ | uses npm
| `ng new` (`@angular/cli`) | ❌ | uses npm
| `create-vite` | ✅ | suggests working deno commands 🎉
| `create-solid` | ❌ | suggests npm commands, needs PR
It's possible that fixing `package-manager-detector` or other packages
might make some of these just work, but haven't looked too carefully at
each
